A main process for producing LEDs today involves a process of metal organic chemical vapor deposition (MOCVD). The process is to grow a quantum well film on a sapphire substrate at several high temperatures. A size of the substrate limits the efficiency of LED production. A current mature technology is to grow quantum well films on 2-inch substrates. If the size of the sapphire substrate is increased from 2 inches to 6 inches, the productivity of LED will be increased by 30%. However, since thermal expansion coefficients of the quantum well film and the sapphire substrate are inconsistent, when the size of the sapphire substrate is increased, a large-sized sapphire substrate is significantly deformed at the time of high temperature growth. Due to such obvious deformation, the sapphire substrate cannot be in perfect contact with a graphite disc, resulting in uneven temperature distribution on the sapphire substrate. A maximum difference in temperature can reach 10° C. The difference in temperature will eventually cause the quantum wells grown at different positions on the sapphire substrate to have different radiation spectrums. The difference in radiation spectrum caused by the difference in temperature can reach 14 nm. This is unacceptable for LED lighting. In order to obtain a quantum well film of uniform thickness, it is necessary to study the two-dimensional morphology of the sapphire substrate and determine a numerical relationship between the two-dimensional morphology and the temperature distribution of the sapphire substrate. At present, there are many methods for detecting the two-dimensional morphology of the sapphire substrate, but only the method of laser macroscopic deformation analysis can be used for real-time and rapid detection of the two-dimensional morphology of the sapphire substrate. The method of laser macroscopic deformation analysis enables two parallel laser beams with known distance to irradiate on a surface of the sapphire substrate. Due to different morphology on the surface of the sapphire substrate, reflection angles of the two laser beams are different. The two laser beams are respectively received by CCDs at known distances from points of incidence of the laser beams, and the CCDs can acquire positions of light spots of the two laser beams. A distance D between the two light spots can be obtained by an image processing method, in combination with a distance d between the two laser beams before arriving at the substrate and a distance Z from the points of incidence to the CCD, a curvature of an arc between the points of incidence of the two laser beams on the sapphire substrate can be calculated.
However, in the MOCVD process, a growth rate of the quantum well film has been greatly improved with the increase of a rotational speed of a graphite disc of the substrate bearing the growth of a wafer epitaxial film, and due to the limitation of a minimum integration time and a reading speed of the CCD, a CCD-based detection technique has been insufficient for detecting a sapphire substrate on a high-speed rotating graphite disc.